Polychromatic printhead

ABSTRACT

This invention relates to a printhead in which a plurality of resistors are selectively activated by an external control circuit to produce the ejection of droplets of ink through nozzles located in correspondence with the resistors. Selection and activation are performed according to a matrix having a plurality of vertical lines corresponding to the number of resistors (1) per group of nozzles and a plurality of horizontal lines corresponding to the number of groups of nozzles (P) in the head. The groups of nozzles (P) in the polychromatic head comprise real nozzles (  1, 27, 53, 79, 131, 157, 183, 235, 261, 287 ) and fictitious nozzles ( 105, 209 ), as a result of which the groups of nozzles have a regular layout, and are uniformly distributed and equivalent to the corresponding layout of a monochromatic head. With this solution, polychromatic heads having the same number and the same disposition of contacts with the external circuit and the same height as a monochromatic head can be manufactured simply.

TECHNICAL FIELD

[0001] This invention relates to a polychromatic printhead comprising aplurality of terminals suitable for being connected to an externalcontrol circuit, a plurality of bars of ink ejection means suitable forbeing selectively controlled by the external control circuit, and aplurality of connections, each suitable for connecting one of theterminals to one of the bars.

[0002] In particular, this invention relates to a polychromatic ink jetprinthead.

BACKGROUND ART

[0003] Monochromatic and polychromatic ink jet printheads of the IDHtype (Integrated Drive Head) are known consisting of an integratedcircuit in which a plurality of thermal resistances or resistors areselectively activated by an external control circuit which transmitsdata or control signals to the head in order to produce the ejection ofdroplets of ink through nozzles located in correspondence with theseresistors.

[0004] The wiring diagram of the known heads 10 (FIG. 1), bothmonochromatic and polychromatic, comprises, arranged in two columns, aplurality of activation groups or primitives 14 each comprising aplurality of resistors 11 and corresponding power transistors 12(addresses I).

[0005] As is disclosed in U.S. Pat. No. 4 864 328 known, each primitive14 is selected and activated by means of contacts P_(J=1+M) (PrimitivesSelect) and each transistor 12 is selected and activated by means ofcontacts A_(I=1+N) (Address Line Select).

[0006] Operation of the known monochromatic and polychromaticheads-consists of the following steps for each column:

[0007] activating for a given time a first address I, for example theaddress I=1, through the contacts A₁;

[0008] electrically feeding a given configuration of primitives withpredetermined current pulses and through the contacts P_(J=1+M);

[0009] activating in sequence a second address I;

[0010] electrically feeding a second given configuration of primitiveswith predetermined current pulses and through the contacts P_(J=1+M);

[0011] and so on in successive steps, until activation of the Naddresses I is completed.

[0012] Whereas the wiring diagrams of the monochromatic andpolychromatic printheads 10 are substantially the same, layout of themonochromatic heads 20 (FIG. 2), especially that of the activationgroups or primitives 24, differs significantly in the known art fromthat of the polychromatic heads 30 (FIG. 3).

[0013] For example, the layout of a monochromatic head 20 (FIG. 2) of312 nozzles comprises two columns of primitives, respectively a columnof 12 odd-numbered primitives 24 and an even-numbered column, whereineach primitive 24 comprises 13 resistors 21 and corresponding nozzles:

312 nozzles=13*12*2

[0014] wherein:

[0015] 13=number of addresses I that may be selected per activationgroup or primitive;

[0016] 12=number of primitives 24 per column; and

[0017] 2=number of columns in the head.

[0018] In particular the layout of the primitives 24 of each column, forexample the odd-numbered column, comprises 12 terminals or contacts 25suitable for being connected to an external circuit and 12 common bars26 of resistors 21 connected to the respective terminals with linearconnections, parallel to one another and uniformly distributed.

[0019] The corresponding layout of the primitives 34 (FIG. 3) of acompatible polychromatic head 30, i.e. having the same height, samenumber and disposition of contacts as the monochromatic head 20 (FIG.2), comprises, for a like number of columns, 288 nozzles arranged inthree colour blocks, respectively block A, B and C (FIG. 3), separatedfrom one another by gaps D needed to physically separate the differentcolour blocks A, B, C.

[0020] Document U.S. Pat. No. 5 455 610 discloses a thermal ink-jetprinter in which two parallel linear arrays of ejectors are subdividedinto sections, the ejectors in each section being adapted to emit ink ofa preselected color.

[0021] For the reasons of compatibility mentioned above, in the knownart the layout of the primitives 34 of each column, for example that ofthe odd-numbered column, comprises 12 terminals or contacts 35 suitablefor being connected to an external circuit and 12 common bars 36 ofresistors 31 connected to the respective terminals.

[0022] In this case, however, according to the known art the common bars36 are different from one another as some are connected to two adjacentcolour blocks with the result that the layout of the connections betweenthe terminals 35 and the common bars 36 is non-homogeneous, non-uniform,and of different length depending on changes to the primitive.

[0023] In addition, as the number of nozzles in the compatiblepolychromatic heads is less than that of the corresponding monochromaticheads, due to the gaps D, the higher order primitives are connected to alimited number of resistors.

[0024] In the example of FIG. 2:

288 nozzles=(13*11*2)+(13*1*2)

[0025] for like addresses, primitives and columns, the higher orderprimitives are connected to a single resistor 31.

[0026] In short, in the known art the layout of the primitives 34 of apolychromatic head 30 is so complex and difficult to produce that insome cases the integrated circuit that constitutes the head must includea conducting layer (metal) in addition to those required for amonochromatic head in order to be able to make the interconnections.

[0027] Besides, in cases of particularly difficult layouts, theterminals corresponding to the higher order primitives of the head arenot connected to the resistors with the result that one of the colourblocks, for instance the colour block C, comprises a lesser number ofresistors and therefore of nozzles than the other colour blocks.

DISCLOSURE OF THE INVENTION

[0028] The object of this invention is to produce a polychromaticprinthead wherein the overall layout, particularly that of theprimitives, has the same characteristics of ease and simplicity ofmanufacturing as in the monochromatic heads while maintaining thecharacteristics of compatibility, such as same number and disposition ofcontacts with the external circuit and same height.

[0029] This object is achieved by the polychromatic printhead whereinthe connections are arranged according to a regular layout equivalent tothe layout of the corresponding connections in a monochromaticprinthead.

[0030] According to another characteristic of this invention, thesolution identified is optimal for polychromatic printheads having anumber of primitives that can be divided by the number of colour blocksenvisaged.

[0031] This and other characteristics of this invention will becomeclear from the description that follows of a preferred embodiment,provided by way of a non-restricting example, and with reference to theaccompanying drawings.

LIST OF FIGURES

[0032]FIG. 1 Represents a wiring diagram of a printhead;

[0033]FIG. 2 represents the layout of a column of primitives of amonochromatic head;

[0034]FIG. 3 represents the layout of a column of primitives of apolychromatic head according to the known art;

[0035]FIG. 4 represents the table of excitation of a column ofprimitives of a monochromatic head;

[0036]FIG. 5 represents the table of excitation of a column ofprimitives of a polychromatic head according to the known art;

[0037]FIG. 6 represents the layout of a column of primitives of apolychromatic head according to the invention; and

[0038]FIG. 7 represents the table of excitation of a column ofprimitives of the head of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0039] The excitation table or grid (FIG. 4) of the odd primitives(first column of nozzles) of a monochromatic printhead 20 (FIG. 2) ofknown type, for example with 312 nozzles, comprises 13 vertical lines(FIG. 4) or addresses and 12 horizontal lines or primitives.

[0040] Assuming, for simplicity's sake, that the odd primitives consistof nozzles with an ascending odd-numbering scheme, the table of FIG. 4shows precisely an example of the sequence in which the ink ejectiondata are transmitted to the various nozzles by the control circuit.

[0041] For example the excitation sequence is as follows:

[0042] a first address is activated by an excitation signal for apredetermined time, for example the address corresponding to the nozzles19, 45, 71, 97, 123, 149, 175, 201, 227, 253, 279, 305;

[0043] a first configuration of odd primitives is electrically suppliedin selective fashion, for example all the primitives in cases ofejection of ink from all the nozzles;

[0044] a second address is activated for a predetermined time, forexample the address corresponding to the nozzles 13, 39, 65, 91, 117,143, 169, 195, 221, 247, 273, 299;

[0045] a second configuration of odd primitives is electrically suppliedin selective fashion, for example all the primitives in cases ofejection of ink from all the nozzles;

[0046] and so on, until completion of all the columns or addresses.

[0047] Naturally there is an equivalent table for the excitation of theeven primitives corresponding to a second column of nozzles of theprinthead; this table is not depicted as it may reconstructed quitesimply by anyone acquainted with the sector art on the basis of thetable in FIG. 4.

[0048] The corresponding table of excitation or grid (FIG. 5) of the oddprimitives (first column of nozzles) of the compatible polychromaticprinthead 30 (FIG. 3), for example with 288 nozzles, again comprises 13vertical lines (FIG. 5) or addresses and 12 horizontal lines orprimitives.

[0049] In this case however, the first 11 primitives comprise 13nozzles, the twelfth primitive, for example primitive 23, comprises asingle nozzle, and furthermore the primitives 7 and 15 comprise nozzlesbelonging to two adjacent colour blocks, depicted in the table in FIG. 5with the numerals of the nozzles in a different background.

[0050] Accordingly:

[0051] the excitation sequence is the same as that described for themonochromatic head only for the first 11 primitives and the primitives 7and 15 concern pairs of adjacent colours;

[0052] the numbering of the nozzles is consistent with the number ofnozzles actually on the head;

[0053] the succession of data and the excitation of the nozzles issequential;

[0054] the layout of the primitives is non-homogeneous and non-uniformto allow for the gaps D.

[0055] With reference to FIG. 6 a polychromatic printhead (head) 60,according to the invention, comprises a plurality of resistors 61 andassociated nozzles, of known type, distributed between numerous colourblocks, for example between three colour blocks, respectively A, B, C,separated by gaps D, respectively D1 and D2, of known type,corresponding to a predetermined number of missing nozzles.

[0056] The head 60 also comprises a plurality of primitives 64 eachcomprising a terminal 65, of known type, and a respective common bar 66connected, in a known way, to a group of resistors 61.

[0057] The terminals 65 of the primitives 64 are connected to therespective common bars 66 with connections of primitives having a layoutequivalent to that of the monochromatic head 20 (FIG. 2), as isdescribed in detail below in a preferred embodiment.

[0058] The colour head 60 of 288 nozzles, according to the example,compatible with the monochromatic head 20 (FIG. 2 and FIG. 6) of 312nozzles, comprises two columns of 144 nozzles in which each column, inturn, comprises three colour blocks, respectively A, B, C of 48resistors 61 and corresponding nozzles and two gaps D1 and D2 of 6missing nozzles or fictitious nozzles.

[0059] In fact:

48*3+6*2=156

[0060] where 156 is the number of nozzles of a column of themonochromatic head 20 with which the colour head 60 of the example iscompatible.

[0061] The common bars 66 of the odd primitives 64 with numbering P1,P3, P5, P11, P13 and P19, P21 and P23 have 13 resistors andcorresponding nozzles, equivalent to the monochromatic head 20.

[0062] The primitives with numbering P7 (FIG. 6) and P17 have 9resistors 61 and the primitives P9 and P15 have 11 resistors 61.

[0063] Thanks to this distribution of the resistors 61, the common bars66 are of constant and uniform length and are equivalent to the commonbars 26 (FIG. 2) of the monochromatic head 20.

[0064] Furthermore, the connections of primitives are also equivalent tothose of the monochromatic head 20 as the terminals 65 (FIG. 6) arelocated on the head, for reasons of compatibility, in the same positionas the terminals 25 (FIG. 2) of the monochromatic head 20 and the commonbars 66 (FIG. 6) are equivalent to those of the monochromatic head 20(FIG. 2).

[0065] Operation of the head 60 (FIG. 6), i.e. the sequence of ejectionof the ink from the various nozzles is illustrated in the table of FIG.7 for the column of odd primitives and corresponding, odd-numberednozzles.

[0066] The numbering of the nozzles corresponds exactly to that (FIG. 4)of the monochromatic head, with the sole difference that some nozzles,in particular those underlined in the table of FIG. 7, i.e. the nozzles97, 99, 101, 103, 105, 107, 205, 207, 209, 211, 213, 215, even thoughincluded in the table, do not correspond to real resistors and nozzles,corresponding instead to the missing nozzles of the gaps D1 and D2 (FIG.6 and FIG. 7).

[0067] The excitation sequence of the head 60 is identical to thatalready described for the monochromatic head, with the sole differencethat some nozzles, being fictitious nozzles, will never be excited,whatever the configuration of primitives powered.

[0068] From the logical viewpoint, the control circuit of the head 60may be compared to that of the monochromatic head and presentsarchitectural differences with respect to the control circuit of theknown polychromatic heads.

[0069] On the basis of the example of embodiment described, therefore:

[0070] the sequence of excitation of the head 60 is identical to thatdescribed for the monochromatic heads;

[0071] the numbering of the nozzles is not consistent with the number ofnozzles actually present on the head and corresponds to that of themonochromatic heads;

[0072] the succession of the data and the excitation of the nozzles isnot sequential in that for some addresses some primitives do not havenozzles, in other words the sequence of excitation comprises data bothfor the real nozzles and for the fictitious ones and the data for thefictitious nozzles are fictitious data, i.e. data specially inserted bythe control circuit in correspondence with the fictitious nozzles inorder to complete the vertical lines of the table in FIG. 7;

[0073] the layout of the primitives is uniformly distributed on the headand corresponds to the layout of the primitives of a monochromatic head.

[0074] From the example described, it is apparent that the layout of theprimitives of the polychromatic heads according to the invention doesnot change when the gaps D and the corresponding number of missingnozzles change.

[0075] In the example the number of primitives of a column may bedivided by the number of colour blocks.

[0076] This condition is optimal in that it permits both to group theprimitives by colour block and not to have primitives with nozzles ofadjacent colours. However, even where the number of primitives cannot bedivided by the number of colour blocks, the solution described remainsvalidly applicable.

[0077] In the example, a head with three colour blocks and two columnsis described, but it is obvious that the colour blocks and the columnsmay be of a different number without altering the characteristics of thesolution described.

[0078] Moreover, the solution described clearly make it possible to use,both for the polychromatic and monochromatic heads irrespectively,certain production fixtures or jigs, such as for example the jigs forthe production of the common bars and for the connections of primitive.

[0079] Changes may be made to the dimensions, shapes, materials,components, circuit elements, connections and contacts, as also to thecircuitry and construction details illustrated and to the method ofoperation without departing from the spirit of this invention.

1. Polychromatic printhead comprising a plurality of terminals (65)suitable for being connected to an external control circuit; a pluralityof bars (66) of ink ejection means suitable for being selectivelycontrolled by said external control circuit; a plurality of connections,each suitable for connecting one of said terminals (65) to one of saidbars (66); characterized in that said connections are disposed accordingto a regular layout corresponding to the layout of said connections in amonochromatic printhead wherein said connections are substantiallyparallel to one another and uniformly distributed.
 2. Printheadaccording to claim 1 characterized in that said bars (66) are grouped soas to form a predetermined number of blocks each having ink ejectionmeans of a predetermined colour.
 3. Printhead according to claim 2characterized in that the number of said terminals (65) is a integermultiple of said predetermined number of blocks.
 4. Printhead accordingto claim 2 or 3 characterized in that said blocks are separated by apredetermined gap corresponding to the predetermined number of missingor fictitious ejection means and in that at least one of the bars (66)adjacent to said gaps, comprises a lower number of ejection means thanthat of the bars (66) not adjacent to said gaps.
 5. Method forcontrolling the ejection of ink in a polychromatic printhead accordingto one of claims 1 to 4, having a plurality of activation groups; and aplurality of ink ejection elements associated with each of saidactivation groups; the method being characterized by the steps of: a)selecting and activating for a predetermined time an element of saidgroups; b) selecting and activating during said predetermined time apredetermined configuration of said activation groups; and of repeatingsaid steps a) and b) until the completion of said plurality of elements;wherein said plurality of elements comprises real and fictitious inkejection elements; and wherein said predetermined configurationcorresponds to the configuration of a monochromatic printhead andcomprises real data associated with said real elements and fictitiousdata associated with said fictitious elements.